Cycling between cameras through python script issue
You can access all objects of the current scene by using bpy.context.scene.collection.all_objects. Then you can filter the objects by their type like lemon suggested, list comprehension makes the code a little shorter. Once you have a list of the cameras you can iterate through them and activate one after another.

import bpy

obj_in_scene = bpy.context.scene.collection.all_objects
cameras = [obj for obj in obj_in_scene if obj.type == 'CAMERA']

for cam in cameras:
    bpy.context.scene.camera = cam
    # Do something else here while this object is the current camera
    print(bpy.context.scene.camera.name)